U.S. patent number 4,630,120 [Application Number 06/563,399] was granted by the patent office on 1986-12-16 for telecine machines.
This patent grant is currently assigned to British Broadcasting Corporation. Invention is credited to Ian Childs.
United States Patent |
4,630,120 |
Childs |
December 16, 1986 |
Telecine machines
Abstract
In a telecine apparatus having a film transport mechanism for
moving a film at a nominally constant speed and including a motor
driving a capstan around which the film passes, there is a sensor
for line-by-line scanning of the film to provide a raster-scanned
electrical output signal representative of the film image. Also
included is a scan control and a film speed measuring device
coupled to the capstan to provide an output representative of the
instantaneous film speed. A compensating device connects the output
of the film speed measuring device to an input of the scan control
such that the scan time of a particular line scanned by the sensor
is varied to compensate for fluctuations in the film speed.
Inventors: |
Childs; Ian (Sutton,
GB2) |
Assignee: |
British Broadcasting
Corporation (London, GB2)
|
Family
ID: |
10529398 |
Appl.
No.: |
06/563,399 |
Filed: |
November 30, 1983 |
PCT
Filed: |
March 29, 1983 |
PCT No.: |
PCT/GB83/00095 |
371
Date: |
November 30, 1983 |
102(e)
Date: |
November 30, 1983 |
PCT
Pub. No.: |
WO83/03513 |
PCT
Pub. Date: |
October 13, 1983 |
Foreign Application Priority Data
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|
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Mar 30, 1982 [GB] |
|
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8209327 |
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Current U.S.
Class: |
348/106;
348/E3.003; 348/E9.009 |
Current CPC
Class: |
H04N
3/38 (20130101); H04N 9/11 (20130101) |
Current International
Class: |
H04N
3/38 (20060101); H04N 3/36 (20060101); H04N
9/11 (20060101); H04N 009/11 () |
Field of
Search: |
;358/214,54,44,215,216,346,348,332 ;360/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0013610 |
|
Mar 1982 |
|
EP |
|
2632378 |
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Jan 1978 |
|
DE |
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1505533 |
|
Mar 1978 |
|
GB |
|
2007935 |
|
May 1979 |
|
GB |
|
2061057 |
|
May 1981 |
|
GB |
|
1597504 |
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Sep 1981 |
|
GB |
|
1604546 |
|
Dec 1981 |
|
GB |
|
2097220 |
|
Oct 1982 |
|
GB |
|
Other References
"Novel Uses of Digital Processing in a Modern Telecine", I. Childs
& M. J. Griffiths, International Broadcasting Convention,
Brighton, U.K., Sep. 18-21, 1982, pp. 46-50. .
"FDL 60-Progress in Film Scanning Using CCD Sensors and Digital
Processing", D. Poetsch et al., `International Broadcast Engineer`,
Jan. 1981, pp. 47-49..
|
Primary Examiner: Lev; Robert G.
Attorney, Agent or Firm: O'Connell; Robert F.
Claims
I claim:
1. Telecine apparatus comprising a film transport mechanism for
moving a film at a nominally constant speed and including a motor
driving a capstan around which the film passes, scan means for
line-by-line scanning of a film to provide a raster-scanned
electrical output signal representative of a film image, scan
control means having an output connected to the scan means to
control the scan, and a film speed measuring device coupled to the
capstan provide an outside representative of the instantaneous film
speed, characterised by compensating means connecting the output of
the film speed measuring device to an input of the scan control
means such that the timing of the line scanned by the scan means is
varied to compensate for fluctuations in the film speed.
2. Apparatus according to claim 1, in which the scan means
comprises a linear light sensor array and provides the lines at a
rate such as to define an instantaneous period between the start of
successive lines, and the scan control means includes means for
automatically varying the periodicity of operation of the scan
means in response to an electrical signal, and the apparatus
includes second compensating means for compensating the magnitude
of the said output signal in inverse relation to the instantaneous
periodicity of the scan means.
3. Apparatus according to claim 1, in which the scan control means
includes means for detecting when the line scan rate required is
less than a predetermined fraction of a nominal scan rate
corresponding to normal viewing of the film, and in response
thereto causes the scan means to increase the line scan rate by a
factor m, and the apparatus includes signal processing circuitry
connected to the output of the scan means to select only one out of
each m generated lines for subsequent processing.
4. Apparatus according to claim 1, in which the scan control means
includes means for detecting when the line scan rate required
exceeds a predetermined maximum rate, and in response thereto
causes the scan means to decrease the scan rate by a factor m
dependent upon the required line scan rate required.
5. Telecine apparatus comprising a linear light sensor array, a
light source, a film transport mechanism for moving film at a
substantially constant rate between the light source and the sensor
array, an optical system for imaging an illuminated section of film
on the sensor array, and scan means for causing the light sensor
array periodically to provide an output signal representative of
the imaged film section, characterised by scan control means for
automatically varying the period of the operation of the scan means
in response to an electrical signal, and compensating means for
compensating the magnitude of the said output signal in inverse
relation to the instanteous periodicity of the scan means.
6. Apparatus according to claim 5, in which the compensating means
additionally compensates for variations in element-to-element
sensitivity in the sensor array.
7. Apparatus according to claim 5, in which the scan control means
includes means for detecting when the line scan rate required is
less than a predetermined fraction of a nominal scan rate
corresponding to normal viewing of the film, and in response
thereto causes the scan means to increase the line scan rate by a
factor m, and the apparatus includes signal processing circuitry
connected to the output of the scan means to select only one out of
each m generated lines for subsequent processing.
8. Telecine apparatus comprising a film transport mechanism, scan
means for line-by-line scanning of the film to provide a
raster-scanned electrical signal representative of the film image,
scan control means having an output connected to the scan means to
control the periodicity of the scan whereby a line scan rate can be
materially varied from a nominal rate corresponding to normal
viewing of the film, and signal processing circuitry connected to
the output of the scan means, characterised in that the scan
control means includes means for detecting when the line scan rate
required is less than a predetermined fraction of the said nominal
rate, and in response thereto causes the scan means to increase the
line scan rate by a factor m, and in that the signal processing
circuitry selects only one out of each m generated lines for
subsequent processing.
9. Apparatus according to claim 8, in which each line selected by
the signal processing means is arranged to be of substantially
constant duration independent of changes in the said required line
scan rate.
10. Apparatus according to claim 8, in which the factor m is a
power of two.
11. Apparatus according to claim 8, in which the scan control means
includes means for detecting when the required line scan rate
exceeds a predetermined maximum rate, and in response thereto
causes the scan means to decrease the scan rate by a factor m
dependent upon the required line scan rate.
12. Telecine apparatus comprising a film transport mechanism, scan
means for line-by-line scanning of a film to provide a
raster-scanned electrical output signal representative of a film
image, scan control means having an output connected to the scan
means to control the periodicity of the scan whereby the line scan
rate can be materially varied from a nominal rate corresponding to
normal viewing of the film, and signal processing circuitry
connected to the output of the scan means, characterised in that
the scan control means includes means for detecting when the line
scan rate required exceeds a predetermined maximum rate, and in
response thereto causes the scan means to decrease the scan rate by
a factor m dependent upon the required line scan rate.
13. Apparatus according to claim 12, in which the lines of each
field of the output signal are derived from m/2 different film
frames in a cyclical sequence.
14. Apparatus according to claim 12, in which the lines of each
field of the output signal are derived from one film frame only and
the signal processing circuitry is operative to generate m lines
from each scanned line.
15. Apparatus according to claim 14, in which the output lines are
derived by repeating lines from the said film frame.
16. Apparatus according to claim 14, in which the output lines are
derived by interpolating from lines of the said film frame.
17. Apparatus according to claim 12, in which m is a power of
two.
18. Telecine apparatus comprising a film transport mechanism, scan
means for line-by-line scanning of a film to provide a
raster-scanned electrical output signal representative of a film
image, and signal processing circuitry connected to the output
signal of the scan means and comprising a digital store capable of
storing at least one field, characterized in that at least when the
film is not moving above a predetermined low value below its
nominal speed the signal processing circuitry is adapted to select
for one part of the image lines derived from one film frame and for
another part of the image lines derived from an adjacent film
frame, there being a junction between the two parts defined by the
line being scanned by the scan means at a particular instant.
19. Apparatus according to claim 18, in which the junction between
the two parts is defined by the lines being instantaneously
scanned.
20. Apparatus according to claim 18, in which the junction between
the two parts is defined by the line being scanned at the beginning
of each television field.
21. Apparatus according to claim 18, in which a blanked line or
lines is formed at the junction.
22. Apparatus according to claim 18, in which the signal processing
means comprises a sequential-to-interlace converter having an input
and an output, and in which at least in one mode of operation of
the apparatus the signal processing circuitry selects for
application to a review output of the apparatus to provide a
displayed picture the interlaced output of the converter for lines
forming one part of the picture and the line at the input to the
converter which is repeated to form another part of the
picture.
23. Telecine apparatus comprising a film transport mechanism, scan
means for line-by-line scanning of a film to provide a
raster-scanned non-interlaced video output signal representative of
a film image, and signal processing circuitry connected to the scan
means and comprising a sequential-to-interlaced converter having an
input and an output for converting the video output signal to an
interlaced output signal, characterized in that at least in one
mode of operation of the apparatus the signal processing circuitry
selects for application to a review output of the apparatus to
provide a displayed picture the interlaced output signal of the
converter for lines forming one part of the picture and the line at
the input to the converter which is repeated to form another part
of the picture.
24. Telecine apparatus comprising:
a linear light sensor array;
a light source;
a film transport mechanism for moving film between the light source
and the sensor array;
an optical system for imaging an illuminated section of film on the
sensor array;
scan means for causing the light sensor array periodically to
provide an output signal representative of an imaged film
section;
scan control means for automatically varying the periodicity of
operation of the scan means in response to an electrical
signal;
a film speed measuring device coupled to the film transport
mechanism to provide an output representative of the instantaneous
film speed;
first compensating means connecting the output of the film speed
measuring device to an input of the scan control means such that
the line scanning is varied to compensate for fluctuations in the
instantaneous film speed; and
signal processing circuitry connected to the scan means and
responsive to the output signal thereof and comprising a
sequential-to-interlaced converter having an input and an
interlaced output and comprising a digital store capable of storing
at least one field, and second compensating means for compensating
the magnitude of the output signal from the scan means in inverse
relation to the instantaneous periodicity of the scan means;
the scan control means including means for detecting when the line
scan rate required is less than a predetermined fraction of the
nominal rate corresponding to normal viewing of the film and in
response thereto the scan means increases the line scan rate by a
factor m and the signal processing circuitry selects only one out
of each m generated lines for subsequent processing;
the scan control means further including means for detecting when
the line scan rate exceeds a predetermined maximum rate and in
response thereto causing the scan means to decrease the scan rate
by a factor m dependent upon the required line scan rate;
the signal processing circuitry, at least when the film is not
moving above a predetermined low value below its normal speed,
being adapted to select for one part of the image lines derived
from one film frame and for another part of the image lines derived
from an adjacent film frame, there being a junction between the two
parts defined by the line being scanned by the scan means at a
particular instant; and
the signal processing circuitry, at least in one mode of operation
of the apparatus, selecting for application to a review output of
the apparatus to provide a displayed picture the interlaced output
of the converter for lines forming one part of the picture and the
line at the input to the converter which is repeated to form
another part of the picture.
25. Apparatus according to claim 1, including means responsive to
the passage of film frames through the film transport mechanism to
provide framing pulses, and means responsive to the framing pulses
to determine a measure of the precise film frame pitch of the film,
whereby film shrinkage can be compensated.
26. Apparatus according to claim 25, in which the means for
providing framing pulses comprises a sprocket roller and a shaft
encoder coupled thereto.
27. Apparatus according to claim 1, including a user-operated
control for inputting a value representing the desired height of
the television image, and in which the scan control means is
responsive to the said value to vary the line scan rate in response
thereto.
28. Apparatus according to claim 2, in which the second
compensating means additionally compensates for variations in
element-to-element sensitivity in the sensor array.
29. Apparatus according to claim 3, in which each line selected by
the signal processing means is arranged to be of substantially
constant duration independent of changes in the said required line
scan rate.
30. Apparatus according to claim 3, in which the factar m is a
power of two.
31. Apparatus according to claim 4, in which the lines of each
field of the output signal are derived from m/2 different film
frames in a cyclical sequence.
32. Apparatus according to claim 4, in which the lines of each
field of the output signal are derived from one film frame only and
the signal processing circuitry is operative to generate m lines
from each scanned line.
33. Apparatus according to claim 32, in which the output lines are
derived by repeating lines from the said film frame.
34. Apparatus according to claim 32, in which the output lines are
derived by interpolating from lines of the said film frame.
35. Apparatus according to claim 4, in which m is a power of
two.
36. Apparatus according to claim 1, including signal processing
circuitry connected to the output of the scan means and comprising
a digital store capable of storing at least one field, and in which
at least when the film is not moving above a predetermined low
value below its nominal speed the signal processing circuitry is
adapted to select for one part of the image lines derived from one
film frame and for another part of the image lines derived from an
adjacent film frame, there being a junction between the two parts
defined by the line being scanned by the scan means at a particular
instant.
37. Apparatus according to claim 36, in which the junction between
the two parts is defined by the lines being instantaneously
scanned.
38. Apparatus according to claim 36, in which the junction between
the two parts is defined by the lines being scanned at the
beginning of each television field.
39. Apparatus according to claim 36, in which a blanked line or
lines is formed at the junction.
40. Apparatus according to claim 36, in which the signal processing
means comprises a sequential-to-interlace converter, and in which
at least in one mode of operation of the apparatus the signal
processing circuitry selects for application to a review output of
the apparatus to provide a displayed picture the interlaced output
of the converter for lines forming one part of the picture and the
line at the input to the converter which is repeated to form
another part of the picture.
41. Apparatus according to claim 1, including signal processing
circuitry connected to the output of the scan means and comprising
a sequential-to-interlaced converter for converting the video
signal to interlaced form, and in which at least in one mode of
operation of the apparatus the signal processing circuitry selects
for application to a review output of the apparatus to provide a
displayed picture the interlaced output of the converter for lines
forming one part of the picture and the line at the input to the
converter which is repeated to form another part of the
picture.
42. Apparatus according to claim 8, including signal processing
circuitry connected to the output of the scan means and comprising
a digital store capable of storing at least one field, and in which
at least when the film is not moving above a predetermined low
value below its nominal speed the signal processing circuitry is
adapted to select for one part of the image lines derived from one
film frame and for another part of the image lines derived from an
adjacent film frame, there being a junction between the two parts
defined by the lines being scanned by the scan means at a
particular instant.
43. Apparatus according to claim 42, in which the junction between
the two parts is defined by the lines being instantaneously
scanned.
44. Apparatus according to claim 42, in which the junction between
the two parts is defined by the line being scanned at the beginning
of each television field.
45. Apparatus according to claim 42, in which a blanked line or
lines is formed at the junction.
46. Apparatus according to claim 8, including signal processing
circuitry connected to the output of the scan means and comprising
a sequential-to-interlaced converter having an input and an output
for converting the video signal to interlaced form, and in which at
least in one mode of operation of the apparatus the signal
processing circuitry selects for application to a review output of
the apparatus to provide a displayed picture, the interlaced output
of the converter for lines forming one part of the picture and the
line at the input to the converter which is repeated forming
another part of the picture.
47. Apparatus according to claim 12, including signal processing
circuitry connected to the output of the scan means and comprising
a digital store capable of storing at least one field, and in which
at least when the film is not moving above a predetermined low
value below its nominal speed the signal processing circuitry is
adapted to select for one part of the image lines derived from one
film frame and for another part of the image lines derived from an
adjacent film frame, there being a junction between the two parts
defined by the line being scanned by the scan means at a particular
instant.
48. Apparatus according to claim 47, in which the junction between
the two parts is defined by the lines being instantaneously
scanned.
49. Apparatus according to claim 47, in which the junction between
the two parts is defined by the line being scanned at the beginning
of each television field.
50. Apparatus according to claim 47, in which a blanked line or
lines is formed at the junction.
51. Apparatus according to claim 12, including signal processing
circuitry connected to the output of the scan means and comparing a
sequential-to-interlaced converter having an input and an output
for converting the video signal to interlaced form, and in which at
least in one mode of operation of the apparatus the signal
processing circuitry selects for application to a review output of
the apparatus to provide a displayed picture, the interlaced output
of the converter for lines forming one part of the picture and the
line at the input to the converter which is repeated to form
another part of the picture.
Description
BACKGROUND OF THE INVENTION
This application concerns various improvements in the field of
telecine machines, and relates to various inventions concerned with
improved operation of the machines. A telecine machine, often
simply termed `a telecine`, is operative to generate a television
signal or at least a video signal from cinematographic film.
There are now available two principal types of telecine machines
which are of interest, namely the linear array type and the flying
spot type. A linear array telecine has a linear array of
light-sensitive elements, namely in the form of a charge coupled
device (CCD), which provides a serial output representing a line of
television signal at a time. The film is driven at a constant rate
between the linear array and a light source in a direction
substantially perpendicular to a plane containing the sensor array,
and an optical system images an illuminated section of film on the
sensor array. Such a telecine machine is described in U.S. Pat. No.
4,275,422.
The flying spot telecine has been available for many years and
comprises an imaging CRT tube on which a spot is illuminated to
provide a scanning light source for the film. A single sensor
device is located on the other side of the film and an optical
system collects the light which passes through the film and images
it onto the sensor device.
With linear-array telecines, it has been proposed to include a
digital store at the output of the telecine to convert non-standard
signals from the sensor array into standard format. It has also
been proposed to use digital stores with flying-spot scanning
telecines.
The following description will initially be made with reference to
a linear-array telecine. However the application of the principles
described is not so limited and they can also be used with flying
spot telecine machines, as is discussed in more detail below in the
detailed description of a preferred embodiment.
DESCRIPTION OF THE PRIOR ART
The way in which a line-array telecine operates is, by now, well
known. Vertical scanning of the film image is accomplishd by the
physical movement of the film. There are several consequences of
this. The first is that the signals emerge from the sensor in a
sequential order, so conversion to standard interlaced form is thus
necessary and this implies the use of digital storage at the output
of the telecine. A second consequence is that the height of the
final television picture can only be adjusted (for a given film
speed) by varying the scan rate of the line-array sensor, and that
this scan rate will also vary between the different film gauges,
because of the different size of the frame bars. Another
consequence is that the nominal scan rate of the sensor should be
related to the nominal film speed, in other words, if the film is
replayed at 18 frames per second, the sensor scan rate will be 0.72
times that at 25 frames per second.
It is thus apparent that the sensor only rarely scans at the same
rate as the television line standard and that a second function of
the digital output store is to provide a buffer between the
incoming scan rate from the sensor and the outgoing scan rate
locked to station syncs. Low sensor scan rates can be accommodated
relatively easily; one convenient approach is to use a fixed clock
frequency and and insert "gaps" of variable numbers of clock pulses
between successive scans. The maximum scan rate of which a sensor
is capable is fixed, however, and so there is a maximum speed at
which a film can be run if the sensor is to scan every line. For
example, the sensor scan rate required by normal aspect ratio 35 mm
film running at 25 frames per second and producing an output
intended for the 625/50 standard is 18.075 kHz (i.e. 1 line every
55.3 microseconds). If a telecine were to be designed with this as
a limit, then 16 mm film could be run at speeds up to 28.9 frames
per second; any increase over these speeds, or any increase in the
displayed picture height, would mean that the sensor could not scan
every line. Thus an alternative must be used.
Earlier proposals, for example British Pat. Nos. 1,597,504 and
1,604,546, have considered these problems and produced solutions
whereby the scanning rate of the line-array sensor and the speed at
which the film is moved can be linked. Both of these earlier
methods are subject to limitations, however. In the case of Patent
No. 1,597,504 the film running speed and sensor scanning rate are
each locked independently to the incoming television synchronising
pulses. Although the parameters of this locking can be varied to
take account of changes in nominal running speed, there is no
method by which any fluctuations in film speed can be corrected
for; thus, until the film transport servo system has settled down
(which might take several seconds) there may be severe framing or
geometric errors on the output television picture.
The system of Patent 1,604,546 is very similar in that, under
locked-up running conditions, both sensor scanning rate and film
motion speed are independently locked to an external reference. In
addition, it allows for a second mode of operation whereby the
sensor scans at a constant high speed and the film is allowed to
move at any speed. Again, however, there is no accommodation of
changes in the film running speed, and the arbitrary way in which
the film is scanned leads to several problems. At low film running
speeds the output television pictures show a random vertical frame
distortion varying from line to line. At medium speeds a join
appears in the television output above which the information comes
from one film frame and below which it comes from an adjacent
frame; this join may roll through the television picture. And
finally, at high film speeds, the random way in which the output
television signal is assembled produces a very disturbing
result.
SUMMARY OF THE INVENTION
The inventor has appreciated that there are a number of
improvements which can be made to the available telecine machines
and these improvements are defined in the appended claims.
In a preferred embodiment of the invention the scan rate of the
line-array sensor is linked directly to the film speed. Ways of
measuring the film speed are already incorporated in a telecine as
part of the film transport servo system. Using the output from
these measuring devices also to drive the sensor scanning circuits
has the result that once the film framing information has been
acquired (which can be achieved when the film is first run after
being laced onto the machine and takes only a few film frames--a
fraction of a second--to complete) any fluctuations in the film
motion can be tracked by the sensor scanning system. Thus any
disturbance caused by starting, stopping and changing speed can be
minimised; ideally the `run-up` time required by the telecine can
be reduced to zero, that is the telecine can be started only when
its output is required by the television system and not several
seconds in advance, as at present.
It will be appreciated that various different outputs may be
required for different purposes. It may be simply that the film is
being scanned for review purposes, e.g. for editing. In this case
the displayed quality need not be particularly high, but scene and
shot changes should be fairly clearly defined. Alternatively, it
may be that a broadcast quality signal is needed, in which case a
higher quality output without flicker or movement judder becomes
important.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail, by way of
example, with reference to the drawings, in which:
FIG. 1 is a block circuit diagram of a linear-array telecine
machine embodying the invention in various of its aspects;
FIG. 2 is a more detailed block diagram of the
sequential-to-interlace store unit 26 of the telecine of FIG.
1;
FIG. 3 is a block circuit diagram similar to FIG. 1 for a
flying-spot telecine;
FIG. 4 is a block circuit diagram of a system for correcting
variations in integration time and in element-to-element
sensitivity of the CCD sensor;
FIG. 5 illustrates a form of display which can be useful for review
purposes;
FIG. 6 illustrates a display in which a portion of the displayed
picture consists of the input to the sequential-to-interlace
converter for use on standby;
FIG. 7 is a perspective view of part of a telecine machine of the
type having a linear array light sensor;
FIGS. 8, 9 and 10 are flow charts illustrating the operation of the
scan microprocessor 12 in response to a tachometer pulse, a
sprocket pulse, and a start of scan pulse respectively; and
FIGS. 11 and 12 are flow charts illustrating the operation of the
control microprocessor 30 in response to an input line and a
request for an output line respectively.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The following description is broken down into different sections
covering the principal important features of the preferred telecine
machine embodying the invention.
1. BASIC VARIABLE-SPEED/HEIGHT CONTROL SYSTEM
A control system for a variable-speed telecine embodying the
invention based on a line-array sensor is shown in FIG. 1. The
system includes a microprocessor 12 which links the servo circuits
38 of the telecine transport 14 to the scan-generating circuit 16
for the CCD sensors 18.
FIG. 7 shows the structure of a line array telecine. The film 116
is moved through the apparatus at a nominally-constant rate by a
capstan 114 driven by an electric motor 122 and is guided by guide
rolls 110, 112. To one side of the film is positioned a light
source 118 and a collector or condensor lens 120. Opposed to the
light source on the other side of the film 116 is the linear light
sensor array 18, aligned parallel to the width of the film, and
onto which light which has passed through the film is imaged by a
lens 124. The sensor 18 has a plurality of sensor elements, e.g.
1024. As the film passes through the light path successive lines in
the film picture are imaged on the sensor, which is scanned to
produce a corresponding television signal.
The upper guide roller 110 carries sprocket teeth 126 which engage
the film perforations 128. The roller 110 is thus positively driven
by the film. A shaft encoder 130 fitted to the end of the sprocket
roller 110 is arranged to emit a sprocket pulse every time a film
frame passes.
The capstan 114 carries a capstan tachometer 132. The tachometer
includes an optical tachometer disc fitted to the shaft of the
capstan to enable the telecine servo units to accurately control
the film speed. The tachometer produces a series of pulses the
frequency of which is directly proportional to the film speed; some
tachometers produce two sets of pulses, the relative phasing
between which can be used to determine in which direction (forwards
or backwards) the film is being driven.
The telecine servo and control circuit 38 includes the usual servo
control loop for controlling the drive motor 122. The circuit 38
provides an electrical output for the scan processor indicating the
film gauge set on the telecine control panel. It is also convenient
to mount other manually-operable selectors on the control panel for
controlling the display parameters, e.g. to initiate the wipe
function described in Section 5 below. The outputs of such
selectors are also applied to the scan processor 12.
Returning to FIG. 1, the microprocessor 12 is fed with the signals
from the capstan tachometer and, from those signals, independently
measures the speed and direction of the film motion. The speed is
measured by counting the number of cycles of the microprocessor
clock frequency (which is usually crystal-controlled and of high
accuracy) which occur between successive tachometer pulses; this
counting may be accomplished either as part of the microprocessor
contol program or by use of a separate counting circuit (the latter
approach is preferred as it gives a greater accuracy). If the
physical dimensions of the film (which may vary slightly due to
film shrinkage and/or manufacturing tolerances) are known
accurately, then the scan rate required to produce television
pictures of the desired height from the particular film gauge used
can be easily calculated.
For example, if the number of microprocessor clock pulses occurring
between successive tachometer pulses is n, if there are N
tachometer pulses produced per revolution of the capstan, and if
the microprocessor clock frequency is f.sub.m Hz, the capstan is
rotating at a rate of f.sub.m /Nn revolutions per second. If the
diameter of the capstan is d.sub.c meters then the film is moving
at a linear speed of .pi.d.sub.c f.sub.m /Nn meters/second.
If the distance between successive frames on the film is l.sub.f
meters then the rate at which the film is being replayed is
.pi.d.sub.c f.sub.m /Nnl.sub.f frames/second. Finally if the height
of the film frame that it is intended should fill the 575 active
lines of the 625/50 television picture is l.sub.a, the scan
frequency f.sub.1 required from the line-array sensor is f.sub.1
given by:
A similar equation can be derived for the 525/60 television
standard, in which the factor 575 is replaced by e.g. 485.
The first factor, 575 l.sub.f /l.sub.a, depends only on the desired
height of the final television image and is a user control. The
second factor, .pi.d.sub.c f.sub.m /Nl.sub.f, is largely constant
for any given machine and film gauge; small variations will occur,
however, due to variations in the film frame pitch, l.sub.f. Such
variations also affect the main telecine servo system and are
measured, in conventional telecines, by incorporating an idling
sprocket wheel driven by the film perforations; this sprocket emits
an electrical pulse once per film frame and examination of this
pulse by the telecine servo system enables the film speed to be
adjusted to compensate for these variations.
As with the capstan tachometer output, the output of this idling
sprocket is fed to the microprocessor 12. The microprocessor can
then calculate the correct value of l.sub.f ; the way in which this
can be done will be described below.
When the microprocessor 12 has calculated the desired scan rate,
information is sent to the waveform generator 16 which produces the
signals required to drive the sensors 18. In order to produce the
signals the waveform generator requires a stable clock frequency at
a frequency determined by the parameters of the line-array sensor;
such a clock frequency is provided by including a further crystal
oscillator (termed the sensor clock oscillator) as part of the
waveform generator. A convenient way of establishing a given sensor
scanning frequency is therefore to count the number of cycles of
this sensor clock oscillator; the information from the
microprocessor 12 thus consists of the desired number of sensor
clock cycles, c.sub.s, in a scan. If the sensor clock frequency is
f.sub.s Hz then the number of sensor clock cycles required per scan
at a scan frequency f.sub.1 is f.sub.s /f.sub.1 or:
clock cycles per scan.
The outputs from the sensors (one for each of the red, green and
blue channels) are corrected for variations in element-to-element
sensitivity in a circuit 20, processed in the normal manner through
a processing channel 22, converted into digital form in
analogue-to-digital converters 24, and then written into a
sequential-to-interlace store 26. An alternative approach, not
shown, is to matrix the RGB signals out of the processing channel
into YUV form before feeding to the analogue-to-digital converters.
This allows some saving in the storage requirement to be achieved
as the U and V signals can be reduced in bandwidth compared to the
Y signal.
The scan microprocessor 12 must send a line and frame number 28 to
the control unit 30 for the sequential-to-interlace converter
(itself another microprocessor) to identify the particular line
being scanned. The sequential-to-interlace converter control unit
30 uses this information to decide where in the store 26 the
particular scan signals should be put so that they may be retrieved
correctly. It is also responsible for retrieving the scan
information in response to station synchronising signals at an
input 34 to provide R,G and B signals at the output 36.
In order for the scan microprocessor 12 to calculate the line and
frame number 38 it is necessary to provide an additional signal 32
from the waveform generator 16 indicating the start of every scan.
On receipt of such a `start of scan` signal the scan microprocessor
calculates the next line to be scanned by incrementing or
decrementing the previous line number by one, depending on whether
the film is running forwards or backwards, and incrementing or
decrementing the frame number if the resulting line number is
either greater than 575 l.sub.f /l.sub.a (forwards running) or less
than 0 (backwards running).
Thus the scan microprocessor 12 must carry out three separate
operations in response to three separate inputs. In response to a
start of scan pulse 32 it must update the line and frame numbers 28
fed to the sequential-to-interlace control unit 30. In response to
a pulse from the capstan tachometer 132 it must calculate the scan
duration information fed to the waveform generator 16. And in
response to a pulse from the idling sprocket shaft encoder 130 it
calculates the film shrinkage information used in the other
calculations.
This shrinkage information, l.sub.f, is calculated by assuming an
initial value. The line and frame numbers being sent to the
sequential-to-interlace control unit at the time that a pulse is
received from the idling sprocket, L.sub.n and F.sub.n, are noted
and compared with the corresponding values from the previous
sprocket pulse, L.sub.n-1 and F.sub.n-1. Ideally L.sub.n should be
the same as L.sub.n-1, and F.sub.n should be either greater by one
or less by one than F.sub.n-1 (depending whether the film is
running forwards or backwards). A line difference, L.sub.n
-L.sub.n-1 (corrected for any additional difference between F.sub.n
and F.sub.n-1) is generated. If this is not zero then clearly the
original value chosen for l.sub.f was in error and a new value
l.sub.f.sup.1 is calculated by the formula:
where A is a constant whose value is chosen to achieve a
satisfactory compromise between an excessively long response time
(A too small) and an unstable response or one excessively sensitive
to short-term fluctuations in the sprocket pulse rate (A too
large). The plus or minus sign depends on whether the film is
running forwards or backwards. A correction can also be made for
any incorrect framing of the film by incorporating an additional
term into the equation:
where F is a number indicating the desired framing relationship of
the film--the line number that should be being scanned at the time
a sprocket pulse is received--and B is a second constant whose
value is subject to similar considerations to A.
A simplification can be made in order to reduce the computational
burden on the scan microprocessor 12. Because the factor l.sub.a
/l.sub.f only changes when the displayed height changes and because
the factor Nf.sub.s /.pi.d.sub.c f.sub.m is a constant for any
given machine the shrinkage information l.sub.f need not be
calculated independently. Instead an initial value for the complete
expression:
is assumed and this value used to replace l.sub.f in equation 3 and
4. If the displayed height is changed while the film is running,
then corrections must be made to this value K to account for the
changing value of l.sub.a /l.sub.f. It is convenient to make these
corrections once per film frame during the interval between film
frames so that errors in picture geometry are not produced in the
television output.
In this way all the critical elements of the control system are
digital and there is a rigid relationship between the film speed
and the scan rate throughout the machine. Thus, once the correct
framing relationship and film shrinkage information has been
acquired it will be maintained whatever the film speed
fluctuations. Broadcast quality signals may thus be generated, in
perfect framing, at all speeds from still frame up to the maximum
rate at which the sensors are capable of operating.
An emergency routine can be included in the scan microprocessor
program to cope with situations where there is a loss of film
framing. Such situations could occur when the film is first laced
onto the telecine or following an extremely poor splice, for
example. A suitable emergency routine would, on receiving a pulse
from the idling sprocket wheel, immediately reframe the television
picture; this would cause a large disturbance in the television
output but it would only last for one film frame.
FIG. 2 shows a more detailed block diagram of the
sequential-to-interlace store unit 26, together with its associated
control microprocessor 30. A main digital store 60 is fed with a
sequence of read and write addresses and incoming data, the latter
being the main signal from analogue-to-digital converters 24. The
size of store required is discussed in U.S. Pat. No. 4,275,422. The
incoming data is written into the storage location specified by the
write address from write address generator 62. Data is read from
the location specified by the read addresses from the read address
generator(s) of which there may be more than one; two separate read
address generators 64 and 66 are shown in FIG. 2. The address
generators 62, 64 and 66 are fed from the control microprocessor
30. The control microprocessor specifies a start address and the
address generators increment this value element-by-element for the
duration of one television line. After this time they stop; the
control microprocessor 30 must then send another start address to
enable the reading or writing process to continue. Thus the storage
is organised in blocks of one television line; if a start address
is not received, or if the microprocessor 30 generates an invalid
line address, the address generator produces a `disable` signal.
This `disable` signal eight prevents the writing process (write
address generator 62) or blanks the relevant data output (read
address generator 64 or 66). This blanking facility can be
useful--one application is described in section 4 below.
The two outputs from the digital store 60 feed an interpolator unit
68. This interpolator combines the two data feeds read under the
control of read address generators 64 and 66 in a proportion
determined by the control microprocessor 30. It can be used to
provide movement interpolation, as in U.S. Pat. No. 4,275,422, or
to provide interpolation between picture lines, as will be
described in section 3 below. The outputs can be subject to
digital-to-analogue conversion in converters 70.
In operation, the sequential-to-interlace control microprocessor 30
is fed with the line and frame number of the incoming scan received
over line 28. It allocates a storage block to that incoming
information and retains the location of that block (or information
enabling it to recalculate the block location) in an internal
memory. An interface is provided between the microprocessor 30 and
the incoming television synchronising pulses on line 34; this
interface generates the line number required for the next
television output line. The control microprocessor 30 then recovers
the store block location of the information that was stored having
the same line number, the appropriate frame number of the
information being calculated in the manner described in U.S. Pat.
No. 4,275,422, and calculates the appropriate interpolation
parameters required.
FIG. 3 shows a modification of the system of FIG. 1 suitable for
use with a flying-spot telecine, the system of FIG. 2 remaining
unaltered. Flying-spot scanners differ in many respects from
line-array scanners; of these only two are relevant here. The first
is that variation of the horizontal scanning rate is more difficult
for a flying-spot machine; in contrast, the ability to alter the
vertical position of the scanning spot makes the vertical scanning
requirements easier. Nevertheless it is clear that there is a
considerable similarity with the system of FIG. 1, and the same
reference numerals are used where appropriate. In contrast to the
line-array control system, it is the delay time between successive
vertical scan intervals from the vertical timebase 52 that is
varied to enable the film speed to be tracked, rather than the
delay between horizontal scan intervals provided by the horizontal
timebase 54. This delay slightly alters the vertical positioning of
the scanned lines. The vertical amplitude of the scanning raster as
provided by the vertical timebase circuit 52 must also be adjusted
but this allows control of the height of the television image
without altering the other scanning parameters; because of this the
televising of non-anamorphic wide-screen films does not lead to the
problems encountered in line-array systems.
With the exception of the compensation for variable integration
time (described below), which is unnecessary for flying-spot
telecines, most other features of the two systems are identical.
The correction circuitry 20 is that appropriate to a flying-spot
telecine. It is still necessary to repeat fields electronically
when the film moves slower than 25 frames per second, although when
the film is moving very slowly it is now possible to generate each
pair of displayed fields from a separate flying-spot scan, making
colour correction of slow-moving or stationary film slightly
easier. Likewise, it is still necessary to interpolate between
lines when the film is moving quickly (as will be described in
section 3 below) because the scan rate of a flying-spot tube is
subject to similar restrictions to that of line-array sensors.
Finally, the output signal will benefit to the same extent from the
movement interpolation described in U.S. Pat. No. 4,275,422 when
the film is running at non-locked speeds.
Thus it will be seen that a method of controlling the scan
formation of either a line-array or a flying-spot telecine is
provided, capable of providing significant improvements in the
variable-speed running characteristics of such machines. In
particular, broadcast quality television pictures may be produced
at up to more than 50 frames per second film speeds (using the
methods described in section 4 below), and pictures adequate for
review purposes may be produced at much higher rates than
this--speeds of 400 frames per second and higher are possible.
2. COMPENSATION FOR INTEGRATION TIME VARIATIONS
This section is specific to line-array telecines and is not
applicable to the flying-spot telecine system of FIG. 3.
With the control system described in section 1 above the sensor
scan rate depends on the running speed of the film. While this
causes no problems with flying-spot telecines, the varying scan
rate causes the integration time of the line-array sensors in
line-array telecines to vary. This in turn causes an apparent
change in sensitivity of the sensors which, uncorrected, would
cause fluctuations in the final television picture. Neither of the
abovementioned British Pat. Nos. 1,597,504 and 1,604,546 mention
the presence of this effect or any mechanism for overcoming it. In
the case of Patent 1,604,546 this is probably because the telecine
manufactured by the patentees used a light valve to control the
light level falling on the line-array sensors; this light valve is
required primarily to adjust the signal level to compensate for
exposure variations on the film, but it would additionally allow
variations in integration time to be compensated for by altering
the brightness of the source illumination. Patent 1,597,504
likewise gives no indication as to how this problem might be
overcome.
A light valve can cause problems because of its relatively slow
response time and additional complexity. The control system of
section 1 above is capable of producing very fast changes in the
integration time of the line-array sensors (faster than those
produced by the systems of the two patents just mentioned) and
these changes might not be compensated sufficiently quickly by a
light valve. For these reasons a more satisfactory solution is
desirable, and in our preferred telecine the variable sensitivity
produced by the changes in integration time is compensated by the
use of a variable-gain amplifier which compensates the magnitude of
the signal in inverse relation to the instantaneous period of the
line scan. Such a variable-gain amplifier is already needed in
order to compensate for variations in element-to-element
sensitivity along the line array; it is now necessary to alter the
range over which this amplifier operates.
FIG. 4 shows a block diagram of the circuit 42 for correcting
variations in integration time and element-to-element sensitivity.
A digital store 80 contains information on the gain required to
compensate the output of the sensor for variations in
element-to-element sensitivity (such compensation is described, for
example, in British Pat. No. 1,526,801). The output from this store
is fed to the digital input of a multiplying digital-to-analogue
converter 82; the analogue input (described below) to this
converter is the compensation for integration time variations. The
digital-to-analogue converter 82 multiplies the two corrections
together and feeds the combined correction signal to one input of
three analogue multipliers 88 (one for each of the R, G and B
channels) whose other input is the output of the linearray sensor.
Each multiplier 88 acts as a variable-gain amplifier and thus
corrects the sensor output for the effects of both
element-to-element sensitivity variations and variations in
integration time.
In order adequately to correct for the effect of variations in
integration time, the compensation input to the multiplying
digital-to-analogue converter 82 must vary according to the
reciprocal of the sensor scanning period. There are two alternative
ways of calculating this reciprocal. The first is to use the scan
microprocessor 12 in the telecine control system to calculate the
correction; this method involves no additional circuitry but places
an extra burden on the speed required of the scan microprocessor.
The second method is to use the scan duration information already
calculated by the scan microprocessor 12 and fed to the CCD
waveform generator to feed a separate shaping circuit which could
use a digital read-only memory 84 to generate the desired
reciprocal, as illustrated in FIG. 4. This digital version of the
correction signal is converted into the analogue form required by
the multiplying digital-to-analogue converter 82 in a second
digital-to-analogue converter 86.
3. DISPLAY AT LOW FILM SPEEDS--USE OF DUMMY SCANS
Some problems remain. One of these is the need to compensate for a
very wide range of integration times; another is that if the
intervals between scans become very long, as they can for low film
speeds, then there is a danger that the sensors may overload. Both
of these problems can be eliminated if the range of integration
times that need to be compensated for is kept as small as possible.
This can be achieved by restricting the range of allowable
integration times to a predetermined factor of for example 2:1. If
the sensor scan rate falls below one half of the maximum value, two
scans are generated and one is discarded; this `dummy` scan is
generated by a suitable program in the scan microprocessor 12 (FIG.
1) and identified as not being a valid scan either by using a
separate signal from the scan microprocessor system to the waveform
generator 16, or, more simply, by merely omitting the label sent to
the sequential-to-interlace microprocessor on line 28. Thus
identified they are then ignored by the sequential-to-interlace
converter system.
More generally, when the required line scan rate is less than a
predetermined fraction of the normal rate, the line scan rate is
automatically increased by an appropriate predetermined factor m,
and only one out of each m lines thus generated are used in the
output signal.
As the film slows down even further, the scan rate of the
line-array sensor again reduces until, eventually, more dummy scans
can be generated. It is convenient to keep the valid scans of fixed
duration (corresponding to the maximum sensor rate) and to vary
only the number and duration of the dummy scans in order to track
film speed variations. If this is done, any errors in the
compensation process for integration time variations will be much
less visible and will be limited to a slight change in intensity
occurring at the critical film speed marking the boundary between
scan rates just more than half the maximum value (no dummy scans
being generated) and scan rates just less than half the maximum
value (dummy scans being generated).
In practice if the film speed is hovering about the critical film
speed there is a danger that slight changes in intensity due to
errors in the compensation operation may be disturbing if the
apparatus is continually changing between normal operation and the
dummy scan mode. It is therefore desirable to introduce a degree of
hysteresis into the system such that the critical film speed at
which the system changes from normal to dummy scan mode is slightly
lower than that at which it changes back from dummy to scan mode to
normal operation.
British Pat. No. 1,604,546 also describes a method of discarding
extra generated scans. This earlier proposal, however, suffers from
several disadvantages. Because of the reliance on a relatively
slow-acting light valve to control the output level of the sensors,
no sudden changes in sensor scan rate can be accommodated. The
sensor is thus operated at a fixed, high scan rate and the nearest
scan to the desired position is chosen as the correct one. The
consequence of this approach is that the final output television
picture may display some geometric instability which, at some
values of film speed, can be disturbing. The Patent does also
mention a rather more controlled approach to discarding the dummy
scans with respect to the generation of television pictures in the
`letterbox` format from Cinemascope films. Again, however, the
small range of operating speed variation tolerated and the lack of
any ability to vary the displayed height of the image represent
severe limitations.
The way in which the dummy scans are generated in our preferred
telecine will now be described. Suppose the c.sub.min is the
minimum number of clock cycles required to complete a full scan at
the highest scan rate and that c.sub.max is the maximum number of
clock cycles required in a valid scan (c.sub.max being greater than
or equal to 2c.sub.min). Firstly the microprocessor 12 checks that
the calculated number of clock cycles per scan required to track
the film speed, c.sub.s, is greater that c.sub.min ; if not the
film is moving too quickly and methods to be described in section 4
below must be used. If c.sub.s is greater than or equal to
c.sub.min the microprocessor then checks if c.sub.s is greater than
c.sub.max ; if c.sub.s is less than c.sub.max then a dummy scan is
not required and a valid scan is carried out. However, if c.sub.s
is greater than or equal to c.sub.max a dummy scan is required; the
microprocessor calculates (c.sub.s - c.sub.min) and examines the
result to see if it is also greater than c.sub.max. If (c.sub.s
-c.sub.min) is greater than or equal to c.sub.max then more than
one dummy scan will be required; and dummy scan of duration
c.sub.min is carried out at the end of which c.sub.s -c.sub.min is
re-examined to calculate further dummy and valid scans. If, however
(c.sub.s -c.sub.min) is less than c.sub.max the following scan will
be a valid one; since we wish to have all valid scans of duration
c.sub.min, the dummy scan must be of duration c.sub.s -c.sub.min.
Following the dummy scan the microprocessor 12 initiates a valid
scan of c.sub.min duration. The program in the
sequential-to-interlace control microprocessor 30 remains unaltered
from that of section 1 above.
While in principle dummy scans could be used in a flying-spot
telecine, as there is in practice no serious problem in reducing
the line scan rate in a flying-spot telecine to very low values,
the use of dummy scans may not be of any real advantage. The
principal interest therefore lies in relation to line array
telecines.
4. OPERATION AT FAST FILM SPEEDS
In a telecine operating with a control system as described in
section 1 above there is a basic difficulty when film is run at
faster than normal speeds. This difficulty is caused by the fact
that the sensor can no longer scan fast enough to track the speed
at which the film is moving. Thus not every line can be scanned on
every film frame.
This fact had been appreciated in British Pat. No. 1,604,546.
However, the system described in that Patent has a major
disadvantage in that the exact relationship between the number of
lines scanned and the number of lines displayed is not subject to
any detailed control but instead is allowed to vary from film frame
to film frame as one set of control pulses changes in phase with
respect to another. Consequently neither of the two possible
display methods produce a pleasing picture. If the missing scan
lines are replaced by adjacent lines in the same frame then the
lack of any frame-to-frame correlation in which lines are repeated
causes moving artefacts on the picture. If, instead, the missing
scan lines are replaced by the corresponding lines of adjacent film
frames then the resultant television picture "tears apart" in areas
of movement, again in an uncontrolled manner.
The control system of section 1 above allows a substantial
improvement to be made in the way that the limited number of scans
available from the line-array sensor are displayed. This
improvement is achieved by controlling the way in which the scan
lines are repeated, by decreasing the line scan rate by a
particular factor (m). For example, if the film is running at
approximately eight times normal speed, the control system can
ensure that lines 1, 9, 17, 25 etc of the television output always
come from the most recent film frame, lines 2, 10, 18, 26 etc from
the film frame before that, lines 3, 11, 19, 27 etc from the film
frame before that and so on. This approach still results in moving
objects splitting into multiple images, but the increased
orderliness in the way in which this splitting is achieved is found
to produce a much more acceptable result.
A further improvement can however be made by generating the missing
scan lines from lines in the same film frame. In the example just
given lines 1, 9, 17 etc. of every film frame would be scanned. At
the start of a television field, the most recent film frame would
be selected and line 1 read out four times (four rather than eight
because each television field contains only half the total number
of lines), line 9 read out four tmes, and so on. Alternatively,
again, an interpolation between lines could be made so that the
television presentation fades from line 1 to line 9 to line 17 and
so on. This interpolation produces an additional loss of vertical
resolution over and above that produced by the increased vertical
movement of the film during the integration time of the sensor; it
also means that events lasting for only a few film frames are
harder to locate. Nevertheless, under most circumstances this
approach produces by far the more acceptable results for review
purposes.
The way in which the control system of FIG. 1 can achieve the
desired operation will now be described. The scan microprocessor 12
calculates the number of sensor clock cycles, c.sub.s, in a scan;
this number is examined to see whether or not it is possible to
achieve a full scan in the allowed time. If not the number is
doubled and the new number examined again; the sequence of doubling
and examination repeats until it is possible to achieve a complete
scan in the required number of clock pulses. Thus the proportion
that is scanned of the total number of lines is restricted to a
binary sequence, i.e. either a half, or a quarter or an eighth
etc., depending on the speed at which the film is running. In order
to enable the sequential-to-interlace converter 26 to reconstruct
the pictures correctly, information about this proportion must be
sent to the sequential-to-interlace control microprocessor 30; this
connection is shown by the dashed lines 40 in FIG. 1. Also
transmitted along this connecton is information to instruct the
sequential-to-interlace control microprocessor 30 as to which sort
of display is required for the output television signal, i.e. lines
repeated from earlier frames, lines repeated from the same frame,
or lines interpolated from the same frame.
The number of times that c.sub.s is required to be doubled is also
required for the calculation of line numbers. If c.sub.s was
doubled three times, for example, that means that only every eighth
line can be scanned. Thus on receipt of a start-of-scan pulse 32
the line number is incremented not by one, as in section 1, but by
eight (or decremented if the film is running backwards). The line
numbers then follow the desired sequence 1, 9, 17, 25 etc. The way
in which the frame number is calculated must also be changed.
If the missing lines are to be generated by repetition or
interpolation of lines from the same frame, then the scan
microprocessor 12 resets the scanning sequence on every new frame
so that the same line numbers are scanned on each film frame (an
exception to this is outlined below). Thus, for example, if the
film is being run forward at eight times normal speed so that lines
1, 9, 17, 25 etc. are scanned then, for 16 mm film presented at
normal height, the final line to be scanned is line number 625.
However, if line 625 was scanned, the first line that could be
scanned on the following film frame would be line number 8; this
would not allow the same sequence of lines to be scanned on all
film frames. This difficulty is overcome by slightly lengthening
the previous scan (line 617) so that line 625 is not in fact
scanned but instead the scan takes place on line 1 of the next film
frame. If the missing lines are to be generated by repetition of
lines from earlier film frames then this scan lengthening procedure
is altered slightly so that the line numbers scanned on each film
frame are not all the same but change from frame to frame in a
preset sequence (e.g. lines 1, 9, 17, 25 on one film frame; lines
2, 10, 18, 26 on the next and so on). A similar procedure is
necessary if the film is accelerating. If every fourth line has
previously been scanned and it now becomes necessary to scan only
every eight lines, a similar jump may be necessary in order to
return to the sequence 1, 9, 17, 25 etc.
The program in the sequential-to-interlace control microprocessor
30 is also modified from that described in section 1. As before,
the incoming scans are stored in blocks of the
sequential-to-interlace store and note is taken of where each line
is stored. However, additional note is also taken of the proportion
of lines scanned on each frame, transmitted along connection 40.
When scans from a given film frame are read out the line number
requested is examined to see if that particular line was originally
scanned. If not, then either the appropriate line from an earlier
film frame is used instead or else the nearest lines from the same
film frame are repeated or interpolated, depending on which mode of
display is required.
While, as noted above, this approach produces acceptable results
for review purposes there are occasions when broadcast-quality
output signals might be required. For example, it might be
desirable to replay film at speeds of just higher than normal (up
to 30 frames per second, for instance) or to increase the displayed
height of film running at 25 frames per second (for example using
1.85:1 aspect ratio film). Under these conditions, where only every
other line is available, it is clearly important to improve the
quality as much as possible. The loss of vertical resolution, in
this instance, is not very severe and may be recovered by suitable
aperture correction after the sensor. This aperture correction may
need different characteristics to more conventional correctors and
will have only the drawback that high-frequency components of the
sensor noise (not the film grain) will be increased. To some extent
this increase in noise will be offset by the increase in signal
gained by the integration of the light over two lines on the film.
A more difficult problem is to make the alias components, produced
by scanning only 312 lines, have as low a visibility as possible.
This can be achieved by altering the approach described above
slightly. The missing lines from any given film frame are sill
interpolated from the lines scanned in that film frame. In
addition, however, the alias components can be broken up by not
always scanning the same lines; for example, on the first film
frame lines 1, 3, 5, 7 etc are scanned and lines 2, 4, 6, 8 etc
interpolated while on the second film frame the situation is
reversed. By this method the aliasing can be made no more
objectionable than that produced by the normal scanning process.
Thus broadcast-quality pictures can be produced from film running
at up to more than 50 frames per second.
5. DISPLAY MODE FOR USE IN REHEARSAL--VERTICAL WIPE
While the control system of section 1 above, with or without the
refinements of sections 2, 3 and 4, is capable of providing an
excellent television display for most normal purposes, there are
circumstances where improvements are possible. One of these is
under low speed `inching` conditions when trying to locate the
exact position of a shot change. At the present time two types of
presentation exist in available telecine machines. One is that used
in the Rank Cintel MkIII flying-spot telecine where the whole
picture `rolls` continuously upwards or downwards; this
presentation makes location of a shot change easy but is unpleasant
to view for any length of time. The second type of presentation,
used in the system of British Pat. No. 1,604,546, is simply to slow
down the rate at which the television picture appears to move; this
type of presentation is also produced by the control system
described in section 1 above. While the second type of presentation
is more acceptable for prolonged viewing it can give the false
impression that the film is running more slowly than it actually is
and the accurate location of a shot change can be surprisingly
difficult. Also, because only one film frame is displayed at a
time, the degree of confidence that the shot change has in fact
been located is usually small.
It is possible to modify the program in the sequential-to-interlace
control microprocessor 30 (FIG. 1) to provide an alternative
display for this case; the program in the scan microprocessor 12 is
not affected.
To provide a display suitable for inching purposes note is taken of
the current position of the scanned line on the film frame (the
line number input on connection 28 to the sequential-to-interlace
control microprocessor is used to provide the necessary data). All
television lines above this position are taken from one film frame
and all television lines below this position are taken from the
adjacent film frame. The effect is to produce the presentation
shown in FIG. 5 where the top part of the picture shows the top
part of the most recent frame and the bottom part of the picture
shows the bottom part of the preceding frame. The display `wipes`
vertically from one frame to the next; one or more lines at the
join 90 between the two scenes can be blanked so as to form a black
line which can be seen even under conditions when both frames
contain the same scene. It has been found convenient to blank about
four lines. With this display there is great confidence that a shot
change has been accurately located--both scenes can be viewed
simultaneously. At the same time the display is not tiring to view
for long periods of time and the rolling black line gives a good
impression of the speed of motion of the film.
In practice it is preferable to note the line being scanned at the
beginning of each television field and to define the join by
reference to that line.
The necessary steps to implement this operation are conducted under
the control of the control microprocessor 30 as shown in more
detail in FIGS. 11 and 12 referred to below.
6. DISPLAY MODE FOR STANDBY USE--SENSOR MONITORING
A second circumstance where the television display is inadequate is
under `standby` conditions, i.e. when the film is stationary or
virtually stationary in the film transport mechanism. This is
because the only television picture available for display is that
contained in the sequential-to-interlace converter store 26. The
operator can then not see if the sensors are still operating (or
more importantly if the film illumination system is still
functioning) and his confidence that the telecine is ready to run
when necessary is reduced. Again, the program in the
sequential-to-interlace control microprocessor 30 can be modified
to provide a display overcoming this problem, without the scan
microprocessor 12 being modified.
A display suitable for use under standby conditions is shown in
FIG. 6. A portion, the lower portion 92 as shown, of the displayed
picture consists of the input line to the sequential-to-interlace
converter store 26, which is being continuously scanned by the CCD
sensor 18, and is thus repeated to occupy the lower portion 92 of
the display. Because the incoming scans are not synchronised to the
television line rate, synchronisation is accomplished in the
sequential-to-interlace store 26; this is achieved by taking note
of the storage block into which the incoming scan is being placed.
If it is a dummy scan and not a valid scan then a separate
additional storage block must be allocated away from the area in
which the rest of the film frame is stored--i.e. all scans are
stored, not just valid scans; only one extra storage block of one
line needs to be allocated, however, as it is not necessary to
retain the dummy scans and they can therefore be allowed to
overwrite each other.
On readout from the store, whenever the television line number is
within a certain range, corresponding in this case to the lower
part of the picture, the output is taken from the most recent input
scan rather than the stored film frame. The program can be arranged
to revert back to normal operation immediately the telecine is
selected `on air`.
The upper portion 94 of the display comes from the output of the
sequential-to-interlace converter 26 and this shows that the store
system is working.
7. MICROPROCESSOR OPERATION
The operation of the scan microprocessor 12 and the control
microprocessor 30 has been indicated in the preceding sections. The
detailed operation of the scan microprocessor is further set out in
FIGS. 8, 9 and 10 which are flow charts showing the required
response of the scan microprocessor 12 to three input stimuli,
namely:
FIG. 8--its response to a tachometer pulse from the tachometer
132,
FIG. 9--its response to a sprocket pulse from the shaft encoder
130,
FIG. 10--its response to a `start of scan` pulse 32.
The detailed operation of the control microprocessor 30 in the
sequential-to-interlaced converter 26 is further set out in FIGS.
10 and 11, which are similar flow charts showing the required
response of the control microprocessor 30 to two inputs,
namely:
FIG. 11--its response to an input line from the scan
microprocessor,
FIG. 12--its response to a request for an output line from the
station synchronising pulses.
The operational steps summarised in these FIGS. 8 to 12 will be
clear from the wording on the figures taken with the pertinent
parts of the foregoing description.
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